Currently there are available techniques for producing SRF cavities with a high accelerating gradient and additional techniques for producing SRF cavities with a high quality factor. Unfortunately, there are no available techniques for producing SRF cavities with both a high accelerating gradient (Eacc) and with a high quality factor (Q0). The meaning of the term “high accelerating gradient (Eacc)” as used herein is an accelerating gradient (Eacc) of 45 MV/m or greater. The meaning of the term “high quality factor (Q0)” as used herein is a quality factor of 4×1010 or greater.
The performance of SRF cavities depend on the process and procedures used in the fabrication of the cavities. Present day methods used barrel polishing, buffer chemical polishing, electro polishing, or a combination of these to remove the surface damage layer that takes place during the preparation of the niobium (Nb) discs and/or deep drawing of half-cells that are welded together to fabricate multi-cell cavities. Unfortunately, these methods tend to produce a damage layer within the niobium cavity which limits the ability to achieve a high Q0. Additionally, chemical polishing loads the cavities with performance degrading hydrogen.
Using high Residual Resistivity Ratio (RRR) niobium with present techniques it is possible to construct accelerator structures with gradients up to about 42 MV/m but low Q0. Under present methods, alloying with nitrogen and titanium improves the Q0 but unfortunately lowers the Eacc.
Accordingly, what is needed is a method for producing high performance accelerator structures, such as SRF cavities, that exhibit a high quality factor (Q0) as well as high accelerating gradients (Eacc). Furthermore, the method should be capable of producing accelerator structures having high Q0 and Eacc cavities at reduced cost in a sustainable way using ingot niobium with relaxed specifications.